Method of making electrical conductors



Patented May 4, 1948 METHOD OF MAKING ELECTRICAL CONDUCTORS Christopher J. Krogel, Cranford, N. J., asslgnor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application July 20, 1943, Serial No. 495,440

8 Claims. 1

This invention relates to a method of making electrical conductors, and more particularly to method of making insulated electrical conductors.

Of recent years and especially in the telephone art electrical conductors having insulation comprising a circumferentially seamless and iongitudinally unbroken sheath of felted fibres of wood, textile substance or the like, have been increasingly employed, particularly in the construction of multi-conductor cables. Such paper pulp sheaths have high insulation value because of the relatively large bulk of air entrapped among and perhaps to some extent within the cellulosic fibres of which they chiefly consist. In some instances, however, it is found that the mechanical weakness of such sheaths is troublesome when these are subjected to tensional and shearing stresses in being handled by machinery during further treatment, such as coating with a waterproof layer, or such as the propelling and guiding means used in intert'wisting conductors together to form a core for a multi-conductor cable. Such pulp sheaths are formed, by several steps usually, from a suspension of the fibres in water directly on the conductive strand into a seamless sheath around the strand. In some instances the conductive strand may be a bare clean wire, so that the sheath is formed directly on the metal surface of the wire. Or the conductive strand may be a wire coated with some shinily hard, tough enamel, generally impervious to and substantially unaffected by water; and the pulp sheath is formed directly on the glossy enamel surface. In such cases there is little adhesion of the pulp sheath to the core on which it is formed, and, consequently, little support for the sheath from the core against tensional, torsional, shearing or bending stresses imposed from without.

An object of the present invention is to provide a method of making an insulated electrical conductor strand, which strand shall comprise a seamless pulp insulating sheath closely adherent to the core which it surrounds and yet retaining all the useful characteristics of such pulp sheaths generally.

With the above and other objects in view, the invention may be embodied in a method of making insulated electrical conductors which comprises steps of coating an electrical conductor with a water emulsion of polyvinyl acetate. forming on the coated body a sheath of waterwet pulp, and drying the coated, sheathed conductor to produce an insulated electrical conductor comprising a conductive core, a coating thereon and adherent thereto of polyvinyl acetate or the like and a sheath out dry interfelted fibres of insulating material on the polyvinyl acetate coating and adherent thereto but no more than superficially penetrated thereby.

Other objects and features of the invention will appear from the following detailed description of embodiments thereof taken in connection with the accompanying drawings in which the same reference numerals are applied to identical parts in the several figures and in which Fig. 1 is a diagrammatic representation of an apparatus for carrying on the method of the invention;

Fig. 2 is an enlarged cross-section of the product of the first step of the method;

Fig. 3 is an enlarged cross-section of the product of the second step of the method;

Fig. 4 is an enlarged cross-section of the product of the third step of the method;

Fig. 5 is an enlarged cross-section of the product of the last method; and

Fig. 6 is an enlarged cross-section of a modifled form of product.

There are shown diagrammatically in Fig. 1 the essential elements only of an apparatus adapted to make insulated electrical wire by carrying out the characterizing steps of the invention. A suitable metal wire is, clean and dry, is passed through a coating unit, generally indicated at 20, where the wire receives a coating l8 of a water emulsion of polyvinyl acetate. Thence the wire is passed to an apparatus generally indicated at 30, in which the wet coated Wire is embedded within a tape 2" of wet felted insulating fibers. In the device generally indicated at 40, the wet tape is rolled and compacted into a seamless cylindrical sheath ll! about the coated wire; and, finally, the sheathed coated wire is dried in the arrangement generally indicated at 50, thus producing the final product shown in Fig. 5 in which the wire 19 and dry pulp sheath ll are held together by the filmlike interposed coating of dry polyvinyl acetate.

The coating unit 20 may be thought of as comprising a pair of opposed nozzles 2| and 22, a supply tank and catch basin 23 thereunder, and a pump 24 to circulate polyvinyl acetate emulsion in water from the tank through the nozzles. The wire iii to be coated passes between the nozzles and then through a pair of suitably grooved rolls 25 and 26 which remove excess coating material from the wire. The pump 24 and rolls 25 and 26 may be driven by a motor 2!.

The tape forming apparatus 30 is not disclosed here in detail f structure and mode of operation since these form no part of the present invention. A suitable apparatus for this purpose is fully disclosed and described in U. S. Patent 1,615,390 of January 2, 1927 to J. S. Little, to which reference may be had if desired.

The device 40 for rolling and compacting the tape into a cylindrical sheath about the core is also no part of the invention insofar as its details of structure and mode of operation are concerned. A suitable device for this step of the method is fully disclosed and described in U. S. Patent 2,312,448 of March 2, 1943 to J. N. Selvig, to which references may be had if desired.

The arrangement 50, used to dry out the water from the coating 2|8 and the wet sheath H1, is also shown diagrammatically nly since its details of structure and operation are no part of this invention. A suitable arrangement for present purposes is fully disclosed and described in U. S. Patent 2.318.533 of May 4, 1943, to which reference may be had if desired.

The wire i9 emerging from the coating unit 20 carries a thin continuous coating 2 I8 of the water emulsion of polyvinyl acetate as shown in Fig. 2. In the apparatus 30, a tape of interfelted, wet pulp is partially formed on the drum, the emulsion coated wire is laid on the partially formed tape, and the formation of the tape 2|! is completed. From the apparatus 30, there emerges the product shown in Fig. 3, a tape of waterwet pulp having the emulsion coated wire embedded in and wholly surrounded by the body of the tape 2|!. In passing through the device 30, the article of Fig. 3 has the tape rolled up and compacted into a substantially cylindrical sheath N1 of wet pulp over the emulsion coating 2|8, as illustrated in Fig. 4. And finally, in passing through the arrangement 50, the water is driven out of both the emulsion coating on the wire and the pulp sheath over the emulsion, so that the final product, shown in Fig. 5, is the electrically conductive core I 9 having the thin, film-like coating of dry polyvinyl acetate adherent thereto, and the sheath of dry, felted, insulating fibres on the polyvinyl coat and adherent thereto.

Because the coating 2| 8 is an emulsion in water, and because the tape 2|! and sheath H! are water-wet pulp, the emulsion does not enter into the pulpg during the formation of the tape 2|! or the rolling up and compacting of the sheath II!. In the product shown in Fig. 4, the emulsion coating 2 i8 is in contact with but not interpenetrant into the wet pulp sheath I". As the water of both the emulsion and the sheath is driven out of these in the arrangement 50, preferably by infra-red radiant heat as described in Patent 2,318,533, this relation continues, and in the final product, shown in Fig. 5, there is firm adhesion of the inner surface of the dry pulp sheath l! to the outer surface of the dry polyvinyl acetate film l8, but no material invasion of the pulp sheath by the polyvinyl acetate, while the dry polyvinyl acetate film also adheres firmly to the wire core.

In place of polyvinyl acetate, polyvinyl alcohol or methyl methacrylate polymer may be used with substantially the same desirable results.

In the illustrative product above described, the conductive core I9 is thought of as a clean bare wire on which the coating I8 is directly placed. There are also enameled wires which it may be desired to insulate further with a pulp sheath. Such wires are those in which the bare metal wire has been coated with a thin layer of usually water resistant and water repellent material such as japan, resinous varnishes, lacquers, of artificial resin, or the like. Despite the water repellent nature of these coatings it is found that when a coated core of this kind is treated with the above described procedure to produce the article shown in cross-section in Fig. 6, the dry polyvinyl acetate coating i8 adheres firmly to the underlying enamel layer IE on the metal wire l9 as well as to the overlying pulp sheath What is. claimed is:

1. The method of making an insulated electrical conductor which comprises steps of coating a conductive core with a water emulsion of material selected from the class consisting of polyvinyl acetate and polyvinyl alcohol and methyl methacrylate polymer, forming on the wet coated core a water-wet sheath of insulating pulp fibres, and drying the coating and the sheath.

2. The method of making an insulated electrical conductor which comprises steps of coating a conductive core with a water emulsion of polyvinyl acetate, forming on the wet coated core a water-wet sheath of insulating pulp fibres, and drying the coating and the sheath.

3. The method of making an insulated electrical conductor which comprises steps of coating a conductive core with a water emulsion of polyvinyl alcohol, forming on the wet coated core a water-wet sheath of insulating pulp fibres, and drying the coating and the sheath.

4. The method of making an insulated electrical conductor which comprises steps of coating a conductive core with a water emulsion of methyl methacrylate polymer, forming on the wet coated core a water-wet sheath of insulating pulp fibres, and drying the coating and the sheath.

5. The method of making an insulated electrical conductor which comprises steps of coating a conductive core with a Water emulsion of material selected from the class consisting of polyvinyl acetate and polyvinyl alcohol and methyl methacrylate polymer, forming on the wet coated strand a tape of water-wet insulating pulp fibres, forming the tape into a water-wet cylindrical sheath about the core, and drying the coating and the sheath.

6. The method of making an insulated electrical conductor which comprises steps of coating a conductive core with a water emulsion of polyvinyl acetate, forming on the wet coated strand a tape of water-wet insulating pulp fibres, forming the tape into a water-wet cylindrical sheath about the core, and drying the coating and the sheath.

7. The method of making an insulated electrica1 conductor which comprises steps of coating a conductive core with a water emulsion of polyvinyl alcohol, forming on the wet coated strand a tape of water-wet insulating pulp fibres, forming the tape into a water-wet cylindrical 5 6 sheath about the core, and drying the coating and the sheath. UNITED STATES PATENTS 8. The method of making an insulated eleo- Number N me Date trical conductor which comprises steps or coat- 1,615,390 Little Jan. 25, 1927 ing a conductive core with a water emulsion of 5 15, 92 Little Jan. 25, 1927 methyl methacryiate polymer. forming on the wet ,41 W lk et 1 'fl 2 1 7 coated strand a tape of water-wet insulating pulp 2,251,296 Shipp Aug. 5, 1941 fibres, forming the tape into a water-wet cy- ,317,725 B1111: Apr. 27, 1943 lindrical sheath about the core, and drying the 2,320,922 Ford June 1, 1943 coating and the sheath. 10 2,325,302 Britt July 27, 1943 CHRISTOPHER J. KROGEL. ,33 ,219 Brown Dec. 7, 1943 REFERENCES CITED The following references are of record in the u file of this patent: 

